As gcc doc [1] shows:
Most optimizations are completely disabled at -O0 or if an -O level is not set on the command line, even if individual optimization flags are specified.
Test result [2] shows, gcc>=11.1.0 deviates from the above description, but before gcc 11.1.0, "-O0" still forcely uses frame pointer in the _start function even if the individual optimize("omit-frame-pointer") flag is specified.
The frame pointer related operations will change the stack pointer (e.g. In x86_64, an extra "push %rbp" will be inserted at the beginning of _start) and make it differs from the one we expected, as a result, break the whole startup function.
To fix up this issue, as suggested by Thomas, the individual "Os" and "omit-frame-pointer" optimize flags are used together on _start function to disable frame pointer completely even if the -O0 is set on the command line.
[1]: https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html [2]: https://lore.kernel.org/lkml/20230714094723.140603-1-falcon@tinylab.org/
Suggested-by: Thomas Weißschuh linux@weissschuh.net Link: https://lore.kernel.org/lkml/34b21ba5-7b59-4b3b-9ed6-ef9a3a5e06f7@t-8ch.de/ Fixes: 7f8548589661 ("tools/nolibc: make compiler and assembler agree on the section around _start") Signed-off-by: Zhangjin Wu falcon@tinylab.org --- tools/include/nolibc/arch-aarch64.h | 2 +- tools/include/nolibc/arch-arm.h | 2 +- tools/include/nolibc/arch-i386.h | 2 +- tools/include/nolibc/arch-loongarch.h | 2 +- tools/include/nolibc/arch-mips.h | 2 +- tools/include/nolibc/arch-riscv.h | 2 +- tools/include/nolibc/arch-s390.h | 2 +- tools/include/nolibc/arch-x86_64.h | 2 +- 8 files changed, 8 insertions(+), 8 deletions(-)
diff --git a/tools/include/nolibc/arch-aarch64.h b/tools/include/nolibc/arch-aarch64.h index 6151be6cd7a9..21e9482a4235 100644 --- a/tools/include/nolibc/arch-aarch64.h +++ b/tools/include/nolibc/arch-aarch64.h @@ -175,7 +175,7 @@ char **environ __attribute__((weak)); const unsigned long *_auxv __attribute__((weak));
/* startup code */ -void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_protector _start(void) +void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void) { __asm__ volatile ( #ifdef _NOLIBC_STACKPROTECTOR diff --git a/tools/include/nolibc/arch-arm.h b/tools/include/nolibc/arch-arm.h index 5b12b6e1c83e..4451bef5f94d 100644 --- a/tools/include/nolibc/arch-arm.h +++ b/tools/include/nolibc/arch-arm.h @@ -225,7 +225,7 @@ char **environ __attribute__((weak)); const unsigned long *_auxv __attribute__((weak));
/* startup code */ -void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_protector _start(void) +void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void) { __asm__ volatile ( #ifdef _NOLIBC_STACKPROTECTOR diff --git a/tools/include/nolibc/arch-i386.h b/tools/include/nolibc/arch-i386.h index 35680b4a25d4..4c94a81e860f 100644 --- a/tools/include/nolibc/arch-i386.h +++ b/tools/include/nolibc/arch-i386.h @@ -190,7 +190,7 @@ const unsigned long *_auxv __attribute__((weak)); * 2) The deepest stack frame should be set to zero * */ -void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_protector _start(void) +void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void) { __asm__ volatile ( #ifdef _NOLIBC_STACKPROTECTOR diff --git a/tools/include/nolibc/arch-loongarch.h b/tools/include/nolibc/arch-loongarch.h index ada5a69e3fcc..590155a4e543 100644 --- a/tools/include/nolibc/arch-loongarch.h +++ b/tools/include/nolibc/arch-loongarch.h @@ -167,7 +167,7 @@ const unsigned long *_auxv __attribute__((weak)); #endif
/* startup code */ -void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_protector _start(void) +void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void) { __asm__ volatile ( #ifdef _NOLIBC_STACKPROTECTOR diff --git a/tools/include/nolibc/arch-mips.h b/tools/include/nolibc/arch-mips.h index dd0f12131b55..d3f0bf4c4245 100644 --- a/tools/include/nolibc/arch-mips.h +++ b/tools/include/nolibc/arch-mips.h @@ -205,7 +205,7 @@ char **environ __attribute__((weak)); const unsigned long *_auxv __attribute__((weak));
/* startup code, note that it's called __start on MIPS */ -void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_protector __start(void) +void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector __start(void) { __asm__ volatile ( /*".set nomips16\n"*/ diff --git a/tools/include/nolibc/arch-riscv.h b/tools/include/nolibc/arch-riscv.h index 1dd7083c2ac8..322c96f4acdb 100644 --- a/tools/include/nolibc/arch-riscv.h +++ b/tools/include/nolibc/arch-riscv.h @@ -180,7 +180,7 @@ char **environ __attribute__((weak)); const unsigned long *_auxv __attribute__((weak));
/* startup code */ -void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_protector _start(void) +void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void) { __asm__ volatile ( ".option push\n" diff --git a/tools/include/nolibc/arch-s390.h b/tools/include/nolibc/arch-s390.h index 8254caff8bfa..587cc91295fa 100644 --- a/tools/include/nolibc/arch-s390.h +++ b/tools/include/nolibc/arch-s390.h @@ -166,7 +166,7 @@ char **environ __attribute__((weak)); const unsigned long *_auxv __attribute__((weak));
/* startup code */ -void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_protector _start(void) +void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void) { __asm__ volatile ( "lg %r2,0(%r15)\n" /* argument count */ diff --git a/tools/include/nolibc/arch-x86_64.h b/tools/include/nolibc/arch-x86_64.h index fb00ab2e9274..5e950a04bc77 100644 --- a/tools/include/nolibc/arch-x86_64.h +++ b/tools/include/nolibc/arch-x86_64.h @@ -190,7 +190,7 @@ const unsigned long *_auxv __attribute__((weak)); * 2) The deepest stack frame should be zero (the %rbp). * */ -void __attribute__((weak, noreturn, optimize("omit-frame-pointer"))) __no_stack_protector _start(void) +void __attribute__((weak, noreturn, optimize("Os", "omit-frame-pointer"))) __no_stack_protector _start(void) { __asm__ volatile ( #ifdef _NOLIBC_STACKPROTECTOR